Pregnant women, vegans and breast-fed babies are among groups for which supplements are commonly recommended.

Kim Painter, USA Today, Jan 18, 2014

Multivitamins and other supplements are not all-purpose elixirs of health: Most studies suggest they don't play a big role in preventing chronic illnesses or extending lives. One recent medical journal editorial called them a flat out waste of money for most consumers. But even the doctors who wrote that editorial, in the Annals of Internal Medicine, said there are exceptions.

What might those be? Experts differ. Below is a rundown on some of the vitamins and minerals that mainstream physicians and dietitians commonly recommend for specific groups.

Here's an important rule of thumb: Treat any supplement like a drug, which has possible benefits but also possible risks, especially if you take too much. Check with your doctor before using it, and always let health professionals know what you are taking.

Folic acid for women of childbearing age

Public health agencies, including the Centers for Disease Control and Prevention, recommend that all women capable of becoming pregnant get 400 micrograms a day of folic acid, from either supplements or fortified foods, such as breads, cereals and pastas. "The reason is that at least half the pregnancies in the United States are unplanned," and folic acid prevents some serious birth defects, including spina bifida, says Edward McCabe, medical director of the March of Dimes. A supplement is a sure way to get it, he says, but "some women feel strongly they can get it from food, and if they really monitor it, that's fine." Some breakfast cereals have the full recommended amount in each serving.

Prenatal vitamins for pregnant women

These contain at least 600 micrograms of folic acid, plus higher levels of iron than typically found in multivitamins, McCabe says. But, he says, the vitamins are not a substitute for good nutrition: "It's extremely important for pregnant women to eat a well-balanced diet."

B-12 supplements for vegans and other groups

Vitamin B-12, which is essential to nerves and blood cells, is found almost exclusively in animal foods - meat, seafood, eggs and milk. So vegans get virtually none in their diets, and some vegetarians may run short, too, if they don't take a supplement or eat fortified foods (including many breakfast cereals, soy milks and nutritional yeast). "Vegans must find a source of vitamin B-12 to be healthy," says Marion Nestle, a professor of nutrition at New York University. Though there's some B-12 in certain seaweeds, they are not a reliable source, according to the Vegan Society and the Vegetarian Resource Group, two educational groups. B-12 supplements also are commonly recommended for people who have gastrointestinal disorders or have undergone weight-loss surgery. That's because their digestive tracts may not adequately absorb the nutrient.

Vitamin D for some babies and seniors

Though vitamin D is a popular supplement, official recommendations are sparse. The American Academy of Pediatrics says all breast-fed babies should take a supplement of 400 IU (international units) a day to prevent bone problems. The U.S. Preventive Services Task Force says a vitamin D supplement can help prevent falls in high-risk adults over age 65. Otherwise, supplements are mostly recommended for people who don't get enough from foods (such as salmon and fortified milk) or sun exposure (a few minutes a day without sunscreen is generally adequate). Expert groups have differed about who should be tested for vitamin D deficiency and how low levels need to be to cause concern. People who might have low levels include those who are obese, have dark skin or have kidney disease or osteoporosis.

Iron supplements for the anemic

Iron deficiency anemia is a common problem, especially among young women. A diet rich in iron - found in meat, beans and many fortified foods - is the best prevention. If your blood levels of iron are low, a doctor may recommend a supplement. But the doctor also should help you find a cause, which could be heavy menstrual bleeding, a gastrointestinal issue or other health problem, says Mariam Pappo, director of clinical nutrition at Montefiore Medical Center in New York. You should not take an iron supplement just because you feel tired, says Heather Mangieri, a registered dietitian in Pittsburgh and spokesperson for the Academy of Nutrition and Dietetics.

Multivitamins for the poorly nourished

The typical U.S. diet might not be ideal, but "most people are not truly deficient" in vitamins, Nestle says. That's why supplements typically don't perform well in studies, she says: "Supplements don't do much for people who are already healthy." Some experts do recommend multivitamins to people whose diets are especially poor and whose habits are hard to change. "There are people who will not eat any fruits or vegetables," Pappo says. "There are people who are sick and can only eat soup and mashed potatoes." Mangieri says "food comes first," but she often works with children and teens who are lifelong "finicky eaters" and who need a multivitamin to tide them over until they learn to enjoy a variety of foods.